Theorem (Ellis & Pinsky): Let $\latex A$, be real symmetric matrices, and assume that is negative semi-definite. Then as :
where , here being the orthogonal projector on the eigenspace of associated with the eigenvalue .
Source: T1270 = S.L.Campbell “On the limit of a product of matrix exponentials”; Linear and Multilinear Algebra; 1978, Vol 6, p.p. 55-59.